From tiny balls of rock to giant egg-shaped objects, there’s a rich and varied array of alien worlds that sit outside the orbit of Neptune. You’re looking at the ones that the European Space Agency’s satellite Herschel has spotted.
In fact, there are 1400 cold worlds in a region of the Solar System beyond the orbit of Neptune, 4.5 — 7.5 billion kilometres from the sun. Herschel has recorded in detail 132 of the things, including their size and albedo (the fraction of visible light reflected from the surface). They’re all incredibly cold, at around — 230C, but they’re otherwise quite different, as the ESA explains:
They range from just below 50 km to almost 2400 km in diameter; Pluto and Eris are the largest. Two worlds have distinctly elongated shapes: Haumea (seen in white) and Varuna (brown). Some even host their own moons (not shown).
The albedo measurement implies a variety of surface compositions: low albedo (brown) is an indication of dark surface materials, such as organic material, while higher albedo (white) suggests pure ices.
These are some of the old remnants of the formation of the Solar System’s planets — and they’re slowly being used to better understand how our little corner of the Universe came into being. [ESA]